Technical Field
The present invention relates to an image projection apparatus, and a system employing interactive input-output capability.
Background Art
Conventional interactive input-output systems can be configured with an image projection apparatus such as a projector, a coordinate input device such as an electronic pen or finger, and an information processing apparatus such as a computer used as an external apparatus. In the interactive input-output systems, a user can draw images (e.g., line, character, text, figure) on a projection screen used for projecting images from the image projection apparatus by using the coordinate input device, and can operate the external apparatus such as the information processing apparatus that transmits image signals by using the coordinate input device on the projection screen. Specifically, a camera is used to calculate or detect coordinates of a point identified or pointed by the coordinate input device on the projection screen. Based on the calculated coordinates of the point pointed by the coordinate input device, the external apparatus such as the information processing apparatus coupled or connected with the image projection apparatus by a communication cable (e.g., USB cable) and a network is operated.
Conventional image projection apparatuses such as rear projection apparatuses employ the following interactive input-output capability, in which the image projection apparatus is coupled or connected to an external apparatus. When the image projection apparatus is projecting an a image on a projection screen such as a wall or white board, a coordinate input device such as a pen can be moved while contacting to the projection screen or not contacting the projection screen, and then based on coordinates of a trajectory of the moved pen, the external apparatus can be operated, or an image can be drawn on the projection screen by using the external apparatus.
As to this image projection apparatus, a plurality of sensors is disposed near the projection screen to calculate distance between the projection screen and the coordinate input device to calculate or detect a point of the coordinate input device relative to the projection screen. When the coordinate input device is operated without touching the projection screen, an image of coordinates pointed by the coordinate input device can be enlarged so that a user (operator) can see a point of the coordinates. With this enlarged condition, even if a movement of the coordinate input device is small, the external apparatus can be operated, or an image can be drawn on the projection screen by using the external apparatus.
However, different from a case that the user operates the coordinate input device by contacting the coordinate input device on the projection screen, when the user operates the coordinate input device without touching the coordinate input device to the projection screen, the user operates the coordinate input device in the space. Therefore, when the user's hand shakes, coordinates input by the coordinate input device becomes unstable and fluctuates. If the coordinates input becomes unstable and fluctuates, coordinates of points on the projection screen cannot be input correctly, which means that coordinates of points matched to the user-intended operation cannot be input, in which the coordinate input error occurs, and thereby the external apparatus cannot be operated, or clear and sharp lines and figures cannot be drawn on the projection screen by using the external apparatus.
Further, when to draw clear and sharp images (e.g., line, character, text, figure) matched to the user-intended operation by using the external apparatus, small or fine movement of the coordinate input device is required to be reproduced on the projection screen, but the coordinate input error may become greater when the user operates the coordinate input device without touching the coordinate input device to the projection screen. Therefore, the clear and sharp images matched to the user-intended operation cannot be generated but unclear and not-sharp images are generated.